1. Field of the Invention
One embodiment of the present invention relates to an insulating pattern and a method of forming the insulating pattern. One embodiment of the present invention relates to a light-emitting device using electroluminescence (EL) and a method of manufacturing the light-emitting device. One embodiment of the present invention relates to a lighting device.
2. Description of the Related Art
A method of forming a thin film pattern is known in which an inverted tapered or T-shaped insulating pattern which has an eaves portion is formed to be used as a separation layer for dividing a film (hereinafter, referred to as “separation layer”). Specifically, a separation layer having an eaves portion is formed and a thin film is formed thereover, whereby a thin film pattern can be formed in which the thin film is not formed in a region covered by a projecting part of the separation layer and the thin film is physically divided.
A method (lift-off method) is well known in which by applying the above technique, a conductive thin film is used as a thin film formed over a separation layer and the separation layer is removed after the thin film is formed, whereby only a conductive thin film pattern remains.
As a method of forming an inverted tapered separation layer, a method in which a negative photosensitive resin is used, light exposure is performed, and development is performed is known.
As a method of forming a T-shaped separation layer, a method (manufacturing method 1) is known in which the amount of light to which a negative photosensitive resin is exposed is smaller and the time of development treatment is shorter than in a usual method, whereby a T-shaped separation layer is formed (Patent Document 1).
As another formation method, a method (manufacturing method 2) is known in which resins with different photosensitivities are stacked, light exposure is performed separately for each of the upper resin and the lower resin with the use of different light-exposure masks, and then development treatment is performed, whereby a T-shaped separation layer is formed.
Further, an organic EL element has been actively researched and developed. In the fundamental structure of the organic EL element, a layer containing a light-emitting organic compound is interposed between a pair of electrodes. By applying voltage to this element, light can be emitted from the light-emitting organic compound.
The organic EL element can be formed into a film form; thus, a large-area element can be easily formed. Therefore, the organic EL element has a high utility value as a surface light source that can be applied to lighting or the like.
For example, a lighting device including an organic EL element is disclosed in Patent Document 2.
[Reference]
    [Patent Document 1] Japanese Published Patent Application No. H9-211868    [Patent Document 2] Japanese Published Patent Application No. 2009-130132
The above-described inverted tapered or T-shaped insulating pattern which has an eaves portion (also referred to as “separation layer”) is left without being removed after a thin film is formed in some cases.
For example, in the case of using the separation layer in a manufacturing method of a light-emitting device using an organic EL element, an EL film and a conductive film are formed over a substrate over which a lower electrode layer and a separation layer are formed to form a pattern in which an EL layer and a conductive layer each divided by the separation layer are stacked; if the separation layer is removed after the stacked-layer pattern is formed, a problem that the EL layer which is an organic film is dissolved is caused. In view of the above problem, it is preferable that the separation layer be left without being removed.
However, depending on the shape of the separation layer having an eaves portion, such as an inverted tapered shape or a T shape, when the coverage with an EL film or a conductive film is high, a thin film is formed on a sidewall of the separation layer and the thin film cannot be surely divided in some cases.
Therefore, it is preferable that a leg portion and a stage portion having an eaves portion which greatly projects beyond the leg portion in the direction parallel to the substrate be included in the separation layer so that a thin film can be divided without fail even in the case where the coverage with the thin film in forming the thin film is high. In particular, a manufacturing method in which the length of the eaves portion of the stage portion, which projects beyond the leg portion, can be controlled is needed. However, a conventional manufacturing method of a T-shaped separation layer has problems described below.
In the manufacturing method 1, a stable shape cannot be obtained on a substrate surface because the amount of light for light exposure and the development time are different from those in a usual method. In addition, there is a problem that the length of a projecting region of a stage portion of a T-shaped separation layer cannot be set to arbitrary length.
In the manufacturing method 2, a stage portion of a T-shaped separation layer can be formed in an arbitrary shape; however, two kinds of resins each having a photosensitivity and light-exposure masks for forming two patterns are needed, which causes a problem of an increase in manufacturing cost.